In recent years, network reach and flexibility has been greatly enhanced through the development and deployment of wireless networks. Among many different wireless protocols are now available (e.g., Wi-Fi, Bluetooth, infrared, various cellular transmission schemes, WiMax, etc.), a large number of wireless networks deployed today employ wireless network components that operate under the IEEE (Institute for Electronic and Electrical Engineers) 802.11 suite of standards.
The most numerous WLAN (wireless local area network) deployments, commonly referred to as “Wi-Fi” (wireless fidelity) networks, employ an air interface operating in the 2.4-gigahertz (GHz) frequency range. The original Wi-Fi standard was developed by the Wireless Ethernet Compatibility Alliance (WECA), and is based on the IEEE 802.11a specification. The IEEE Standard provides support for three different kind of PHY layers, which are an InfraRed (IR) baseband PHY, a frequency-hopping spread spectrum (FHSS) and a direct-sequence spread spectrum (DSSS) PHY operating at either 2.4 GHz or 5 GHz frequency band. For IEEE 802.11b, this results in a bandwidth of up to 11 megabits per second (Mb/s) when an appropriate signal strength is available. IEEE 802.11g defines a similar standard to Wi-Fi, with backward compatibility to 802.11b. However, 802.11g employs orthogonal frequency-division multiplexing (OFDM) rather than DSSS, and supports bandwidth up to 54 Mb/s. Enhanced implementations of 802.11g are asserted by their manufacturers to support transfer rates of up to 108 Mb/s. WLAN equipment employing the IEEE 802.11a standard has also been recently introduced. The 802.11a standard employs a 5 GHz air interface using an OFDM carrier.
A typical 802.11 WLAN deployment implemented with a single wireless access point (AP) 100 is shown in FIG. 1. Wireless AP 100 provides WLAN connectivity to various WLAN stations (STA) within its coverage area 102 via a respective 802.11 link, as depicted by notebook computers 104 and 106, desktop computers 108 and 110, and hand-held wireless device 112 (e.g., personal digital assistants (PDAs), pocket PCs, cellular phones supporting 802.11 links, etc.). (For illustrative purposes, coverage area 102 is shown as a circular shape, although in practice, the actual shape of a particular coverage area will generally vary based on various obstacles and signal interference from external sources.) To support station-side operations, each station provides an appropriate WLAN interface, such as depicted by a PCMCIA 802.11b, g, or a card 114 for notebook computer 106 or an 802.11b, g, or a peripheral expansion card 116 for desktop computer 110. Optionally, the IEEE 802.11 wireless interface may be built-in, such as is the case with notebooks employing Intel's Centrino® chipset. Similarly, wireless handheld devices (e.g., 112) will provide built-in IEEE 802.11 interfaces.
In most deployments, a wireless AP is deployed to extend the reach of a network, such as a LAN, WLAN (wide LAN) or MAN (Metropolitan Area Network). Accordingly, AP 100 is depicted as being linked to a switch 118 via an Ethernet (IEEE 802.3) link 120. In general, switch 118 is representative of various types of switches and routers present in a typical LAN, WLAN or MAN. In some cases, the switching operations may be facilitated via a server 122 that runs software to manage the network and perform software-based switching/routing operations.
A group of stations coordinated by Distributed Coordination Function (DCF) or Point Coordination Function (PCF) is called a basic service set (BSS). In the Infrastructure mode, the AP facilitates and coordinates communication and channel access between stations, and provides access mechanisms for the stations to access various land-based networks via network infrastructure connected to an AP, such as depicted by switch 118, enterprise network 124 and Internet 126. Stations authenticated and associated with an AP do not operate in an ad-hoc mode where peer-to-peer communication is done without connectivity to the AP. Thus, in the infrastructure mode, the AP serves as a central controller and coordinators for data traffic between stations within its coverage area by providing a routing function on the WLAN side. Furthermore, an AP provides another routing function pertaining to the routing of downlink traffic originating from an upstream network (such as enterprise network 124 and Internet 126, as well as traffic originating from other APs) and destined for a WLAN station served by the AP.
In general, stations in an IEEE 802.11 WLAN are not allowed to transmit frames directly to one another and should always rely on the AP for the delivery of frames. However, the IEEE has recently ratified a draft Standard (IEEE P802.11e/D13.0, January 2005) defining Quality of Service (QoS) enhancements for 802.11 Medium Access Control (MAC) layer. According to Section 11.7, stations with QoS facility (QSTAs) may transmit frames directly to another QSTA by setting up such a data transfer using the DLS (Direct Link Set-up) protocol.
In connection with support for direct links between stations, security measures have also been defined under the IEEE P802.11e/D13.0 draft Standard. However, the security measures are insufficient to support direct links with adequate security levels.